Fluid control valve, fluid control device, and protection method for fluid control valve

Abstract

According to the present invention, a fluid control valve uses a piezo actuator that is formed by layering a plurality of piezo stacks. The fluid control valve applies drive voltage to the actuator to make the piezo stacks extend and contract and thereby makes a valve body contact and separate from a valve seat. To disperse the stress that acts on the piezo stacks during extension and contraction and suppress deterioration of a piezo stack that is close to the valve body, a first drive voltage that is applied to the piezo stack that is closest to the valve body is, over at least a prescribed period, lower than a second drive voltage that is applied to any one of the other piezo stacks.

Description

Fluid control valve, fluid control device, and method for protecting fluid control valve

[0001] The present invention relates to a fluid control valve, a fluid control device, and a method for protecting a fluid control valve.

[0002] Patent Document 1 describes a fluid control valve that adjusts the valve opening by applying a drive voltage to a piezoelectric actuator formed by stacking a plurality of piezoelectric stacks to expand and contract the piezoelectric stacks.

[0003] By configuring multiple piezo stacks to expand and contract in this way to adjust the valve opening, the stress acting on the piezo stack during expansion and contraction can be dispersed more effectively than in a configuration in which the valve opening is adjusted by expanding and contracting a single piezo stack.

[0004] However, since piezo stacks are susceptible to deterioration under high temperatures and high voltages, when the above-mentioned piezo actuator is used to control a high-temperature fluid, the piezo stack closest to the flow path of the fluid, in other words, the piezo stack closest to the valve body that constitutes the fluid control valve, becomes hotter than the other piezo stacks, and there is a risk that, for example, the piezo stack will short-circuit due to deterioration, impairing the function of the entire fluid control valve.

[0005] Japanese Patent Application Laid-Open No. 2020-089037

[0006] Therefore, the present invention has been made to solve the above-mentioned problems, and its main objective is to suppress deterioration of the piezo stack close to the valve body while dispersing the stress acting on the piezo stack during expansion and contraction.

[0007] That is, the fluid control valve according to the present invention comprises a valve seat, a valve body that moves toward and away from the valve seat, and an actuator that is formed by stacking a plurality of piezo stacks and to which a drive voltage is applied to drive the valve body, and is characterized in that a first drive voltage applied to the piezo stack closest to the valve body is lower than a second drive voltage applied to any one of the other piezo stacks for at least a predetermined period of time.

[0008] In this type of fluid control valve, by stacking multiple piezo stacks, it is possible to distribute the stress acting on the piezo stacks during expansion and contraction. Also, because the first drive voltage applied to the piezo stack closest to the valve body is lower than the second drive voltage applied to any one of the other piezo stacks, it is possible to suppress deterioration of the piezo stack closest to the valve body even when controlling a high-temperature fluid.

[0009] Preferably, the first drive voltage is lower than the drive voltages applied to any of the other piezo stacks for at least a predetermined period of time, so that the first drive voltage applied to the piezo stack closest to the valve body is the lowest of the drive voltages applied to the other piezo stacks, thereby more reliably suppressing deterioration of the piezo stack closest to the valve body.

[0010] The thermal effect of the high-temperature fluid can extend not only to the piezo stack closest to the valve disc, but also to other piezo stacks closer to the valve disc. Specifically, the closer the piezo stack is to the valve disc, the greater the thermal effect it can have. Therefore, it is preferable that the actuator has three or more piezo stacks, and that the drive voltage applied to the piezo stack closest to the valve disc among the other piezo stacks is lower than the drive voltage applied to the piezo stack farther from the valve disc, at least for a predetermined period of time. In this case, for example, by changing the drive voltage depending on the distance from the valve disc, it is possible to suppress deterioration of each piezo stack other than the piezo stack closest to the valve disc while taking into account the thermal effect.

[0011] In order to reduce the number of parts and costs, it is preferable that the plurality of piezo stacks are connected in parallel to a common power supply.

[0012] It is preferable to provide a voltage dividing circuit between the power supply and the piezo stack closest to the valve body, which allows the first drive voltage to be lower than the second drive voltage with a simple circuit configuration.

[0013] However, even if a voltage divider circuit is used, if the base voltage of the first and second drive voltages becomes high, the first drive voltage also becomes high, and there is a risk that deterioration of the piezo stack close to the valve body may not be suppressed as much as desired. Therefore, it is preferable to provide a constant voltage circuit interposed between the power supply and the piezo stack closest to the valve body to keep the first drive voltage lower than the second drive voltage. In this case, even if the base voltage becomes high, the first drive voltage is kept below a predetermined voltage, so deterioration of the piezo stack close to the valve body can be more reliably suppressed.

[0014] However, even if the first drive voltage is lower than the second drive voltage for a predetermined period of time, if a first drive voltage higher than the second drive voltage is applied for a long period of time during other periods, deterioration of the piezo stack close to the valve body cannot be suppressed as much as desired. Therefore, it is preferable that the average value of the first drive voltage applied during the drive period from the start to the end of drive of the actuator is lower than the average value of the second drive voltage applied during that drive period. In this case, the first drive voltage is lower on average than the second drive voltage during the drive period in which a drive voltage is applied to the piezo stack, thereby suppressing deterioration of the piezo stack close to the valve body.

[0015] Furthermore, the fluid control valve according to the present invention includes a valve seat, a valve element that moves toward and away from the valve seat, and an actuator formed by stacking a plurality of piezo stacks and to which a drive voltage is applied to drive the valve element, wherein of two piezo stacks included in the plurality of piezo stacks, the drive voltage applied to the piezo stack closer to the valve element is lower than the drive voltage applied to the piezo stack farther from the valve element. With such a fluid control valve, stacking a plurality of piezo stacks makes it possible to distribute the stress acting on the piezo stacks during expansion and contraction, and also makes it possible to prevent the piezo stack closer to the valve element from deteriorating more quickly than the piezo stack farther from the valve element.

[0016] Furthermore, a fluid control valve according to the present invention is characterized in comprising a valve seat, a valve disc that moves toward and away from the valve seat, an actuator formed by stacking a plurality of piezo stacks and that drives the valve disc when a drive voltage is applied, a diagnostic piezo stack that is stacked closer to the valve disc than the actuator, and a deterioration diagnosis circuit that applies a diagnostic voltage different from the drive voltage to the diagnostic piezo stack. With such a fluid control valve, by stacking a plurality of piezo stacks, it is possible to distribute the stress acting on the piezo stacks during expansion and contraction, and by diagnosing the deterioration of the piezo stack that is closer to the valve disc than the actuator using the diagnostic piezo stack and the deterioration diagnosis circuit, it is possible to predict the degree of deterioration of the piezo stack that is closer to the valve disc among the piezo stacks that make up the actuator and suppress the deterioration of that piezo stack when controlling a high-temperature fluid.

[0017] It is preferable to have a sensor that detects leakage current from the piezo stack closest to the valve body when the diagnostic voltage is applied, so that a decrease in the internal resistance of the piezo stack closest to the valve body can be used as an indication of the degree of deterioration of that piezo stack.

[0018] Furthermore, a fluid control device according to the present invention is characterized by including the above-mentioned fluid control valve. Such a fluid control device can achieve the same effects as the above-mentioned fluid control valve.

[0019] In addition, a method for protecting a fluid control valve according to the present invention is a method for protecting a fluid control valve comprising a valve seat, a valve element that moves toward and away from the valve seat, and an actuator that is formed by stacking a plurality of piezo stacks and to which a drive voltage is applied to drive the valve element, wherein a first drive voltage applied to the piezo stack closest to the valve element is lower than a second drive voltage applied to any one of the other piezo stacks for at least a predetermined period of time. According to this method, stacking a plurality of piezo stacks makes it possible to distribute stress acting on the piezo stacks during expansion and contraction, and because the first drive voltage is lower than the second drive voltage, it is possible to suppress deterioration of the piezo stack closest to the valve element even when controlling a high-temperature fluid.

[0020] Furthermore, a method for protecting a fluid control valve according to the present invention is a method for protecting a fluid control valve including a valve seat, a valve disc that moves toward and away from the valve seat, and an actuator formed by stacking a plurality of piezo stacks and to which a drive voltage is applied to drive the valve disc, characterized in that a diagnostic voltage different from the drive voltage is applied to a diagnostic piezo stack that is stacked closer to the valve disc than the actuator. According to this method, by stacking a plurality of piezo stacks, it is possible to distribute the stress acting on the piezo stacks during expansion and contraction, and by diagnosing deterioration of the piezo stack closer to the valve disc than the actuator using the diagnostic piezo stack and a deterioration diagnosis circuit, it is possible to predict the degree of deterioration of the piezo stack that is closer to the valve disc than the actuator, and to suppress deterioration of that piezo stack when controlling a high-temperature fluid.

[0021] According to the present invention configured in this manner, it is possible to distribute the stress acting on the piezo stack during expansion and contraction, while suppressing deterioration of the piezo stack close to the valve body.

[0022] FIG. 1 is an overall schematic diagram of a fluid control device according to a first embodiment of the present invention. FIG. 2 is an overall schematic diagram of a fluid control valve according to the same embodiment. FIG. 3 is a circuit diagram of a drive circuit according to the same embodiment. FIG. 4 is a circuit diagram of a drive circuit according to a modified example of the same embodiment. FIG. 5 is a circuit diagram of a drive circuit according to a modified example of the same embodiment. FIG. 6 is a circuit diagram of a drive circuit according to a modified example of the same embodiment. FIG. 7 is an overall schematic diagram of a fluid control valve according to a second embodiment. FIG. 8 is a schematic diagram of a drive circuit and a degradation diagnosis circuit according to the same embodiment.

[0023] <Device Configuration of First Embodiment> A first embodiment of a fluid control valve 3 according to the present invention will be described with reference to the drawings.

[0024] The fluid control valve 3 of this embodiment is used in a fluid control device 100 that controls the flow rate of a fluid such as a process gas supplied to a chamber in, for example, a semiconductor manufacturing process.

[0025] As shown in FIG. 1, the fluid control device 100 includes a block 1 in which an internal flow path FC is formed, a flow rate detection mechanism 2 that detects the flow rate of the fluid flowing through the internal flow path FC, a fluid control valve 3 that controls the fluid, a drive circuit 331 electrically connected to the fluid control valve 3, a housing 4 that houses the flow rate detection mechanism 2, the fluid control valve 3, and the drive circuit 331, and a control unit 5 that controls the operation of the fluid control valve 3.

[0026] A flow rate detection mechanism 2, a fluid control valve 3, and a housing 4 are attached to the block 1. In this embodiment, a high-temperature (e.g., 100°C or higher) process gas flows through the internal flow path FC of the block 1, and the block 1 is heated to a high temperature by a heater (not shown) to prevent the gas from being cooled.

[0027] The flow rate detection mechanism 2 has a thermal flow rate detection sensor, and measures the flow rate of the process gas flowing through the internal flow path FC. The flow rate detection sensor may be a differential pressure type, a Coriolis type, an ultrasonic type, or the like.

[0028] The fluid control valve 3 is a piezoelectric valve that controls the process gas in the internal flow path FC, and is provided here downstream of the flow rate detection mechanism 2. The fluid control valve 3 may also be provided upstream of the flow rate detection mechanism 2.

[0029] As shown in FIG. 2 , the fluid control valve 3 is a normally closed type fluid control valve that includes a valve seat 31, a valve element 32, a piezoelectric actuator 33, a plunger 34, and a casing 35, and is configured so that the valve element 32 moves toward and away from the valve seat 31 as the piezoelectric actuator 33 expands and contracts.

[0030] More specifically, the piezo actuator 33 is held at one end of the casing 35 and extends to the other end of the casing 35, thereby pushing the valve element 32 via the plunger 34 and creating a distance between the valve seat 31 and the valve element 32. Here, the other end of the casing 35 is the side where the block 1 in which the internal flow path FC is formed is provided (in other words, the side where the valve seat 31 and the valve element 32 are provided).

[0031] The piezo actuator 33 has a plurality of piezo stacks X that expand and contract when a drive voltage greater than 0 V is applied, and these piezo stacks X are stacked along the expansion and contraction direction of the piezo actuator 33. When a drive voltage is applied from the drive circuit 331, these piezo stacks X expand and contract, causing the piezo actuator 33 to expand and contract.

[0032] As shown in Fig. 2, the piezo actuator 33 of this embodiment includes three piezo stacks X1, X2, and X3 arranged in this order from bottom to top along the vertical direction. Here, the upward and downward directions respectively indicate the directions toward one end and the other end of the casing 35. The valve seat 31 and the valve element 32 are arranged below the piezo stack X1, and the piezo stack X1 is the piezo stack X closest to the valve element 32 in this example. Although the piezo stacks X in Fig. 2 are arranged along the vertical direction, they may also be arranged in a direction intersecting the vertical direction, for example, along the horizontal direction.

[0033] The piezo stack X is formed by stacking a plurality of piezo elements, for example, and the piezo stacks X are arranged in a row so as to expand and contract in the same direction.

[0034] Furthermore, the piezo actuator 33 of this embodiment is equipped with three piezo stacks X with uniform dimensions and performance, but the dimensions and performance may differ for each piezo stack X, and it is sufficient for the piezo actuator 33 to be equipped with two or more piezo stacks X.

[0035] 2, the drive circuit 331 applies a drive voltage to each piezo stack X. This drive voltage is controlled in response to a drive signal from the control unit 5, which will be described later. In this embodiment, the drive voltages applied to the three piezo stacks X1, X2, and X3 are distinguished by being called drive voltages V1, V2, and V3, respectively.

[0036] As shown in FIG. 3, the drive circuit 331 also has a common power supply PS to which the piezo stacks X are connected in parallel.

[0037] The control unit 5 is a computer equipped with a CPU, memory, an input / output interface, etc., and by causing the CPU and peripheral devices to cooperate in accordance with a predetermined program stored in a predetermined area of ​​the memory, it has the functions of at least a flow rate calculation unit 51 and a valve control unit 52, as shown in Fig. 2. The control unit 5 in this embodiment is housed in the housing 4.

[0038] As shown in FIG. 1, the flow rate calculation unit 51 calculates the flow rate of the process gas flowing through the internal flow path FC based on the output value of the flow rate detection mechanism 2 .

[0039] As shown in FIG. 1 , the valve control unit 52 outputs a drive signal to the drive circuit 331 based on the set flow rate input from outside and the calculated flow rate calculated by the flow rate calculation unit 51, and applies a drive voltage to each piezo stack X to adjust the valve opening of the fluid control valve 3.

[0040] In this embodiment, below the piezo actuator 33 there is an internal flow path FC through which high-temperature process gas flows, and a block 1 heated by a heater to prevent the gas from liquefying. The piezo stack X1, which is located closest to these and closest to the valve body 32, is more likely to reach a high temperature than the other piezo stacks X2 and X3.

[0041] The fluid control valve 3 is configured such that, among the multiple piezo stacks X of the piezo actuator 33, the drive voltage V1 applied to the piezo stack X1 closest to the valve body 32 is defined as a first drive voltage, and the drive voltage V2 or V3 applied to one of the other piezo stacks X2 or X3 is defined as a second drive voltage. The first drive voltage is lower than the second drive voltage for at least a predetermined period. In particular, in this embodiment, both drive voltages V2 and V3 are second drive voltages. That is, the drive voltage V1 is configured to be lower than the drive voltages V1, V2, and V3 applied to each of the piezo stacks X1, X2, and X3 (the first drive voltage is the lowest of the drive voltages applied to the piezo stacks). However, the first drive voltage does not need to be the lowest of the drive voltages applied to the piezo stacks X; it only needs to be lower than the second drive voltage applied to at least one of the other piezo stacks X.

[0042] The predetermined period may be any period long enough to suppress deterioration of the piezo stack X1 closest to the valve body 32 more than deterioration of the other piezo stacks X2 and X3, and may be, for example, at least half the drive period from the start to the end of drive of the actuator. Here, the drive period may be the period from the start of application of a drive voltage to the end of application of the drive voltage, or the period from the start of application of a pulsed drive voltage multiple times to the end of application of the drive voltage multiple times, or may be, for example, the period required for one step in a semiconductor manufacturing process.

[0043] Alternatively, the predetermined period may be a period during which a high drive voltage V2 or V3 (second drive voltage) is applied to the piezo stack X2 or X3, for example, a period during which the difference between the rated voltage of the piezo stack X and the second drive voltage is equal to or less than a certain value, or a period during which the ratio of the rated voltage to the second drive voltage is equal to or less than a certain value.

[0044] However, even if the first drive voltage is made lower than the second drive voltage for a predetermined period of time, if a first drive voltage higher than the second drive voltage is applied for a long period of time during other periods, the deterioration of the piezo stack X1 close to the valve body 32 cannot be suppressed as much as desired.

[0045] Therefore, it is preferable that the average value of the first drive voltage applied during the drive period of the actuator is lower than the average value of the second drive voltage applied during the drive period.

[0046] In this embodiment, as shown in FIG. 3, a voltage divider circuit C1 is provided between a power supply PS that applies a drive voltage to each piezo stack X and the piezo stack X1 that is closest to the valve body 32, thereby making the drive voltage V1 (first drive voltage) lower than the drive voltages V2 and V3 (second drive voltages).

[0047] The drive voltage V1 applied from the power supply PS via the voltage divider circuit C1 to the piezo stack X1 closest to the valve body 32 is the first drive voltage, and the drive voltage V2 or V3 applied from the power supply PS to the other piezo stack X2 or X3 without passing through the voltage divider circuit C1 is the second drive voltage. When the first drive voltage is applied in this way, the predetermined period is the entire period during which the drive voltage is applied from the power supply PS to each piezo stack X.

[0048] Here, this voltage-dividing circuit C1 has two resistors RA with the same resistance value, and the drive voltage V1 (first drive voltage) is half the drive voltages V2 and V3 (second drive voltages). Note that the type and number of resistors RA constituting the voltage-dividing circuit C1 may be changed as appropriate to obtain a desired first drive voltage. The resistors RA may be variable resistors.

[0049] <Effects of First Embodiment> With the fluid control valve 3 of this embodiment configured as described above, by stacking a plurality of piezo stacks X, it is possible to distribute the stress acting on the piezo stacks X during expansion and contraction, and since the first drive voltage is lower than the second drive voltage, it is possible to suppress deterioration of the piezo stack X1 close to the valve body 32 even when controlling a high-temperature fluid.

[0050] Here, as another configuration for preventing deterioration of the piezo stack X1 closest to the valve body 32, it is also conceivable to place a spacer or the like between the piezo stack X1 closest to the valve body 32 and the internal flow path FC and the block 1. In comparison, with the fluid control valve 3 of this embodiment, the first drive voltage that is lower than the second drive voltage but greater than 0 V can be applied to the piezo stack X1 closest to the valve body 32, so that it is possible to both save space and ensure the expansion and contraction amount of the piezo actuator 33 while preventing deterioration of the nearest piezo stack X1.

[0051] In addition, in this embodiment, since the average value of the first drive voltage applied during the drive period is lower than the average value of the second drive voltage applied during the drive period, deterioration of the piezo stack X1 close to the valve body 32 can be suppressed.

[0052] Furthermore, since a plurality of piezo stacks X are connected in parallel to a common power supply PS, the number of parts and costs can be reduced.

[0053] Furthermore, since a voltage dividing circuit C1 is provided between the power supply PS and the piezo stack X1 closest to the valve body 32, the first drive voltage can be made lower than the second drive voltage with a simple circuit configuration.

[0054] Incidentally, in a piezo actuator 33 in which multiple piezo stacks X are connected in parallel to a common power supply PS, if even one piezo stack X fails, such as by a short circuit, the function of the entire piezo actuator 33 is impaired, even if the other piezo stacks X are normal. As described above, piezo stacks X deteriorate quickly when a high voltage is applied in a high-temperature environment, and the piezo stack X1 closest to the valve body 32 is prone to becoming hot. However, with the fluid control valve 3 of this embodiment, the drive voltage V1 (first drive voltage) is lower than the drive voltages V2 and V3 (second drive voltages), so it is possible to avoid the piezo stack X1 closest to the valve body 32 failing earlier than the other piezo stacks X2 or X3, which would impair the function of the entire piezo actuator 33.

[0055] <Modification of First Embodiment> In the above embodiment, the voltage divider circuit C1 is used to make the first drive voltage lower than the second drive voltage, but other methods may be used.

[0056] For example, the piezo actuator 33 may be provided with multiple power supplies PS, each generating a first drive voltage and a second drive voltage from a different power supply PS. This allows the first drive voltage, lower than the second drive voltage but higher than 0 V, to be freely generated over a predetermined period of time. This allows the expansion and contraction of the piezo stack X1 closest to the valve body 32 to be freely adjusted and used to adjust the valve opening, while also preventing deterioration of the piezo stack X1. Even if the piezo stack X1 closest to the valve body 32 were to short-circuit due to deterioration, the piezo actuator 33 as a whole can be driven by the other piezo stack X2 or X3 because it is not connected to a power supply in parallel with the other piezo stacks X2 or X3. In this case, the predetermined period can be freely set.

[0057] 4, instead of the voltage divider circuit C1, a constant voltage circuit C2 that maintains the drive voltage V1 (first drive voltage) lower than the drive voltages V2 and V3 (second drive voltages) may be interposed between the power supply PS and the piezo stack X1 closest to the valve body 32. If the voltage divider circuit C1 is used to generate the first drive voltage, the first drive voltage will also become high when the base voltage of the drive voltage increases. On the other hand, if the constant voltage circuit C2 is used to generate the first drive voltage, the first drive voltage will not exceed a predetermined voltage, so deterioration of the piezo stack X1 closest to the valve body 32 can be more reliably suppressed even if the base voltage increases.

[0058] The predetermined voltage may be set to a value smaller than the rated voltage of the piezo stack X. Alternatively, it may be set based on the drive voltage required to maximize or minimize the valve opening. In this case, the predetermined period is the period during which the source voltage of the drive voltage is higher than the predetermined voltage set by the constant voltage circuit C2.

[0059] A specific circuit configuration of the constant voltage circuit C2 may be one that uses a Zener diode ZD. Note that the constant voltage circuit C2 may also be one that uses, for example, a three-terminal regulator.

[0060] Furthermore, in order to make the drive voltage V1 (first drive voltage) lower than the drive voltages V2 and V3 (second drive voltages), as shown in FIG. 5, a Zener diode ZD, for example, may be connected in series to the piezo stack X1 closest to the valve body 32, or as shown in FIG. 6, a resistor RA may be connected in series to the piezo stack X1 closest to the valve body 32 and the Zener diode ZD.

[0061] 6, the Zener diode ZD is disposed on the power supply side, but the relative positions of the elements may be changed as appropriate. In these cases, the predetermined period is the entire period during which the drive voltage is applied from the power supply PS to each piezo stack X.

[0062] In the above embodiment, the voltage divider circuit C1 maintains the first drive voltage at a value greater than 0 V for a predetermined period of time. However, the first drive voltage may be 0 V. In other words, applying the first drive voltage may also mean not applying the drive voltage for a predetermined period of time. This more reliably suppresses deterioration of the piezo stack X1 near the valve body 32.

[0063] Furthermore, a configuration may be adopted in which a drive voltage is not always applied to the piezo stack X1 closest to the valve disc 32; for example, the piezo stack X1 may not be connected to the power supply PS. In this case, the piezo stack X1 closest to the valve disc 32 is not connected to the power supply in parallel with the other piezo stacks X2 and X3. Therefore, even if the piezo stack X1 closest to the valve disc 32 is short-circuited due to heat, the valve opening adjustment function of the entire piezo actuator 33 is not impaired. Furthermore, in this case, by simply changing the circuit configuration, the piezo stack X1 closest to the valve disc 32 can be used as a spacer without significantly changing the structure of a conventional fluid control valve, and deterioration of the other piezo stacks X close to the valve disc 32 can be suppressed.

[0064] In the above embodiment, attention is focused only on the first drive voltage applied to the piezo stack X1 closest to the valve disc 32, but the thermal effect of the high-temperature fluid may extend not only to the piezo stack X1 closest to the valve disc 32, but also to the other piezo stacks X2 and X3 close to the valve disc 32. Specifically, the piezo stack X2 second closest to the valve disc 32 may be subjected to the second greatest thermal effect.

[0065] Therefore, when the piezo actuator 33 has three piezo stacks X as in the above embodiment, it is preferable that, of the remaining piezo stacks X2 or X3, the drive voltage V2 applied to the piezo stack X2 closest to the valve body 32 is lower, at least for a predetermined period of time, than the drive voltage V3 applied to the piezo stack X3 farthest from the valve body 32. In this way, it is possible to suppress deterioration not only of the piezo stack X1 closest to the valve body 32, but also of the piezo stack X2 second closest to the valve body 32.

[0066] Alternatively, the first drive voltage may be applied collectively to a plurality of continuously stacked piezo stacks X, including the piezo stack X1 closest to the valve body 32. For example, the drive voltages V1 and V2 applied to the piezo stacks X1 and X2 in the above embodiment may be the first drive voltage. In this case, deterioration of the plurality of piezo stacks X arranged closer to the valve body 32 can be suppressed collectively.

[0067] The piezo actuator 33 in the above embodiment is composed of three piezo stacks X1, X2, and X3, but the number of piezo stacks X constituting the actuator may be two, four or more, as long as there is more than one.

[0068] In the above embodiment, a configuration has been described in which the average value of the first drive voltage applied during the drive period is lower than the average value of the second drive voltage applied during the drive period. However, even if such a configuration is not adopted, it is sufficient that the first drive voltage is lower than the second drive voltage during a predetermined period, thereby suppressing deterioration of the piezo stack X1 close to the valve body 32.

[0069] Although the fluid control valve 3 in the above embodiment is of a normally closed type, it may be of a normally open type.

[0070] In the above embodiment, the first drive voltage that is lower than the second drive voltage applied to at least one of the other piezo stacks X is applied to the piezo stack X1 closest to the valve body 32, but instead, the piezo stack X may be configured such that, of two piezo stacks X included in the plurality of piezo stacks X, the drive voltage applied to one piezo stack X closer to the valve body 32 is lower than the drive voltage applied to the other piezo stack X farther from the valve body 32. Even with this configuration, stacking the plurality of piezo stacks X makes it possible to distribute the stress acting on the piezo stacks X during expansion and contraction, and to prevent the one piezo stack X closer to the valve body 32 from deteriorating more quickly than the other piezo stack X farther from the valve body 32.

[0071] <Device Configuration of Second Embodiment> Next, a second embodiment of the fluid control valve 3 according to the present invention will be described with reference to the drawings.

[0072] The fluid control valve 3 of the second embodiment differs from that of the first embodiment in that it further includes a diagnostic piezo stack Y and a deterioration diagnosis circuit C3, and in that the control unit 5 has a deterioration diagnosis function. These differences will be explained below, and explanations of common parts will be omitted as appropriate.

[0073] 7, the fluid control valve 3 of the second embodiment includes a diagnostic piezo stack Y that is stacked closer to the valve body 32 than the piezo actuator 33. The diagnostic piezo stack Y of this embodiment is located below the piezo actuator 33 and is sandwiched between the piezo actuator 33 and the valve body 32. The diagnostic piezo stack Y of this embodiment is provided integrally with the multiple piezo stacks X that constitute the piezo actuator 33, but may be provided as a separate body.

[0074] Degradation diagnosis circuit C3 applies a diagnostic voltage D, separate from the drive voltage, to this diagnostic piezo stack Y. As shown in FIG. 8 , degradation diagnosis circuit C3 has a power supply PS2 to which the diagnostic piezo stack Y is connected, and a current sensor A that detects leakage current from this diagnostic piezo stack Y.

[0075] Here, the leakage current is a current that flows through the diagnostic piezo stack Y and increases as the diagnostic piezo stack Y deteriorates and its resistance decreases.

[0076] As shown in FIG. 7 , this degradation diagnosis circuit C3 applies a diagnostic voltage D to the diagnostic piezo stack Y in response to a diagnostic signal from the control unit 5, which will be described later. When the diagnostic voltage D is applied, the current sensor A detects the current leaking from the diagnostic piezo stack Y and outputs a signal indicating the detected value to the control unit 5. The diagnostic voltage D may be applied to the diagnostic piezo stack Y at a predetermined voltage continuously or intermittently. Alternatively, it may be applied only when diagnosis is desired. The diagnostic voltage D is preferably lower than the drive voltage so as to prevent the diagnostic piezo stack Y from rapidly deteriorating.

[0077] In this embodiment, as shown in FIGS. 7 and 8, the driving circuit 331 is not connected to the diagnostic piezo stack Y, and no driving voltage is applied thereto.

[0078] The control unit 5 of the second embodiment has at least the functions of a flow rate calculation unit 51 , a valve control unit 52 , a diagnostic voltage control unit 53 , a memory unit 54 , and a degradation diagnosis unit 55 .

[0079] Diagnostic voltage control section 53 outputs a diagnostic signal to degradation diagnostic circuit C3 based on a diagnostic command input from the outside, and controls diagnostic voltage D.

[0080] The memory unit 54 stores a reference value for diagnosing the degree of deterioration of the piezo stack X.

[0081] The degradation diagnosis unit 55 compares the detection value indicated by the signal from the degradation diagnosis circuit C3 with a reference value stored in the memory unit 54 to diagnose the degree of degradation of the diagnostic piezo stack Y. The degradation diagnosis unit 55 outputs the degree of degradation of the diagnostic piezo stack Y as a diagnostic result. In addition, the degradation degree of the piezo stack X that constitutes the piezo actuator 33 may be predicted from the degree of degradation of the diagnostic piezo stack Y and output as a diagnostic result.

[0082] <Effects of Second Embodiment> With the fluid control valve 3 of this embodiment configured as described above, by stacking a plurality of piezo stacks X, it is possible to distribute the stress acting on the piezo stack X during expansion and contraction. In addition, by using the degradation diagnosis circuit C3 to diagnose degradation of the diagnostic piezo stack Y that is stacked closer to the valve body 32 than the piezo actuator 33, it is possible, when controlling a high-temperature fluid, to predict the degree of degradation of the piezo stack X that is closest to the valve body, among the piezo stacks X that constitute the piezo actuator 33, and suppress degradation of that piezo stack X.

[0083] In addition, since a sensor is provided to detect leakage current from the diagnostic piezo stack Y, a decrease in the internal resistance of the diagnostic piezo stack Y can be used for diagnosis as an indication of the degree of deterioration of the piezo stack X that constitutes the piezo actuator 33.

[0084] <Modification of the Second Embodiment> In the above embodiment, no drive voltage is applied to the diagnostic piezo stack Y, but a drive voltage may be applied.

[0085] In the above embodiment, only one diagnostic piezo stack Y is disposed below the piezo actuator 33, but additional diagnostic piezo stacks Y may be disposed in the same position or in other positions. For example, if the additional diagnostic piezo stack Y is disposed above the piezo actuator 33, it is possible to predict the degree of deterioration of the piezo stack X located farther from the valve body among the multiple piezo stacks X constituting the piezo actuator 33, and to know the difference in the degree of deterioration between the piezo stacks closer to the valve body. Furthermore, if the additional diagnostic piezo stack Y is disposed between the multiple piezo stacks X constituting the piezo actuator 33, it is possible to predict the degree of deterioration of the two piezo stacks X adjacent to the additional diagnostic piezo stack Y.

[0086] According to the present invention, by stacking multiple piezo stacks, it is possible to distribute the stress acting on the piezo stacks during expansion and contraction. Furthermore, since the first drive voltage applied to the piezo stack closest to the valve body is lower than the second drive voltage applied to any one of the other piezo stacks, it is possible to suppress deterioration of the piezo stack closest to the valve body even when controlling a high-temperature fluid.

[0087] REFERENCE SIGNS LIST 100...Fluid control device FC...Internal flow path 1...Block 2...Flow rate sensor 3...Fluid control valve 31...Valve seat 32...Valve body 33...Piezo actuator 331...Drive circuit 4...Housing 5...Control unit C1...Voltage dividing circuit C2...Constant voltage circuit C3...Deterioration diagnosis circuit PS...Power supply PS2...Power supply A...Leakage current sensor X...Piezo stack X1...Piezo stack closest to valve body X2...Other piezo stack X3...Other piezo stack Y...Diagnostic piezo stack

Claims

1. A valve seat; a valve body that moves toward and away from the valve seat; an actuator formed by stacking a plurality of piezo stacks, to which a drive voltage is applied to drive the valve body; A fluid control valve, characterized in that a first drive voltage applied to the piezo stack closest to the valve body is lower than a second drive voltage applied to any one of the other piezo stacks for at least a predetermined period of time.

2. 2. The fluid control valve according to claim 1, wherein the first drive voltage is lower than the drive voltages applied to any of the other piezo stacks for at least a predetermined period of time.

3. the actuator has three or more piezo stacks; 2. The fluid control valve according to claim 1, wherein a drive voltage applied to a piezo stack closer to the valve body among the other piezo stacks is lower than a drive voltage applied to a piezo stack farther from the valve body, at least for a predetermined period of time.

4. 3. The fluid control valve according to claim 1, wherein the plurality of piezo stacks are connected in parallel to a common power source.

5. 4. The fluid control valve according to claim 3, further comprising a voltage dividing circuit interposed between a power source that applies a drive voltage to each of the piezo stacks and the piezo stack that is closest to the valve body.

6. 4. The fluid control valve according to claim 3, further comprising a constant voltage circuit interposed between a power supply that applies a drive voltage to each of the piezo stacks and the piezo stack that is closest to the valve body, the constant voltage circuit keeping the first drive voltage lower than the second drive voltage.

7. 4. The fluid control valve according to claim 1, wherein an average value of the first drive voltage applied during a drive period from the start of drive of the actuator to the end of drive is lower than an average value of the second drive voltage applied during the drive period.

8. A valve seat; a valve body that moves toward and away from the valve seat; an actuator formed by stacking a plurality of piezo stacks, to which a drive voltage is applied to drive the valve body; Among two piezo stacks included in the plurality of piezo stacks, A fluid control valve, characterized in that a drive voltage applied to a piezo stack closer to the valve body is lower than a drive voltage applied to a piezo stack farther from the valve body.

9. A valve seat; a valve body that moves toward and away from the valve seat; an actuator formed by stacking a plurality of piezo stacks, to which a drive voltage is applied to drive the valve body; a diagnostic piezo stack stacked on a side closer to the valve body than the actuator; a deterioration diagnostic circuit that applies a diagnostic voltage different from the drive voltage to the diagnostic piezo stack.

10. 10. The fluid control valve according to claim 9, further comprising a sensor that detects leakage current from the piezo stack closest to the valve body when the diagnostic voltage is applied.

11. A fluid control device comprising a fluid control valve as described in claim 1, 8 or 9.

12. A method for protecting a fluid control valve comprising: a valve seat; a valve element that moves toward and away from the valve seat; and an actuator that is formed by stacking a plurality of piezo stacks and to which a drive voltage is applied to drive the valve element, the method comprising: A method for protecting a fluid control valve, wherein a first drive voltage applied to the piezo stack closest to the valve body is lower than a second drive voltage applied to any one of the other piezo stacks for at least a predetermined period of time.

13. A method for protecting a fluid control valve comprising: a valve seat; a valve element that moves toward and away from the valve seat; and an actuator that is formed by stacking a plurality of piezo stacks and to which a drive voltage is applied to drive the valve element, the method comprising: A method for protecting a fluid control valve, comprising applying a diagnostic voltage different from the drive voltage to a diagnostic piezo stack stacked closer to the valve body than the actuator.